1. Field of the Invention
The present invention relates to a disc cartridge for recording information in a recording disc and more particularly to a recording disc comprising a mechanism for positioning the recording disc with a high accuracy.
2. Description of the Prior Art
There has been known to the public magnetic disc cartridges comprising a generally thin rectangular cartridge case and a flexible magnetic recording disc rotatably assembled in the cartridge case by means of a core member to which the recording disc is secured.
FIG. 1 shows a part of a conventional magnetic recording disc of the type mentioned above, in which a magnetic disc assembly 2 for recording and reproducing information is rotatably assembled in a cartridge case 1. The magnetic disc assembly 2 is comprised of a magnetic disc 3 for recording of annular shape, a disc supporting plate 4 of annular shape made of stainless steel plate and having the magnetic disc 3 secured on the outer peripheral edge of the plate 4, a cylindrical hub 5 made of plastic resin material, being provided on the inner peripheral edge of the disc supporting plate 4 by outsert molding, and an annular regulating rib 6 projected from the disc supporting plate 4 near the outer peripheral area of the disc supporting plate 4. The recording disc 3 is made of a base film 3a of polyester film and magnetic layers 3b which may be formed on one of the surfaces of the film 3a or formed on both surfaces as shown in FIG. 2.
Referring to FIG. 1 again, a disc drive assembly 8 of a disc drive device (not shown) is composed of a shaft 9, a disc supporting table 10 rotated with the shaft 9 and an annular permanent magnet 11 fitted to the disc supporting table 10. The disc supporting plate 4 is secured on the top surface of the disc supporting table 10, the top surface of which serves as a reference surface, by the magnetic force of the permanent magnet 11. Thus, the recording disc 3 can be placed in position in the direction of the thickness of the recording disc 3. The inner part of the lower surface of the disc supporting plate 4 serves as a contacting surface for contacting the reference surface of the disc supporting table 10 and the outer part of the upper surface of the disc supporting plate 4 serves as a securing surface for securing the inner peripheral portion of the recording disc 3.
As shown in FIG. 1, in the conventional disc cartridge, the contacting surface and the securing surface are formed on both opposite surfaces of the disc supporting plate 4. Therefore, the securing surface changes relative to the contacting surface depending on the error of the thickness of the disc supporting plate 4' resulting in changing the position of the recording disc 3. Since the amount of movement of the recording head of the disc drive device to the recording disc is controlled based on the reference surface of the disc supporting table 10, if the recording disc 3 is displaced by the error of the thickness of the disc supporting plate 4, the contact pressure of the recording head to the recording disc 3 changes, thereby contact between the recording head and the recording disc become worse.
On the other hand, in the conventional disc cartridge of the above type, the regulating rib 6 faces to the drive shaft insertion opening 12 of the cartridge case 1 so that the disc assembly 2 is prevented from being unduly displaced in the cartridge case 1 up to such extent that the recording disc is damaged by clash of the outer peripheral portion of the recording disc with the inner surface of the cartridge case 1 even if the disc cartridge is vibrated during transportation of the disc cartridge or the like.
Furthermore, the hub core 5 is comprised of V shaped regulating walls (not shown) in the drive shaft insertion opening 12 to center the drive shaft 9 relative to the center of the hub core 5. Also, the disc supporting plate 4 is clamped on the reference surface of the disc supporting table 10 by the magnetic force of the permanent magnet 11 defining the vertical position of the disc assembly 2.
In the conventional disc cartridge, the hub core 5 and the rib 6 are formed by separate members, the hub assembly being complicated in construction and therefore, reduction of the size and weight of the hub assembly is prevented.
Furthermore, the magnetic pulling portion of the permanent magnet 11 is formed in the space between the outer peripheral portion of the hub core 5 and the rib 6, however, as the disc cartridge is made small, the space for the magnet must be also reduced, therefore size of the magnet 11 must be reduced, thereby resulting in reduction of the force of clamping the recording disc 3.
The conventional disc drive apparatus is so arranged such that the position of the disc assembly 2 in the disc drive device in the vertical direction is constrained by the top surface of the disc supporting table 10 and the disc assembly is centered by engagement between the cylindrical surface of the spindle 9 and the V shaped walls of hub core 5. This means that the reference surfaces for positioning the disc assembly are made of combination of two individual members, therefore the reference surfaces change due to an error of size of each components per se and an assembling error, whereby a stable and accurate drive of the recording disc can not be assured.